OBJECTIVE: To review the scientific literature on several dietary supplements and herbal products commonly promoted for weight loss. DATA SOURCES: Recently published articles and abstracts identified through PubMed (May 1987-May 2003), MEDLINE (January 1966-May 2003), International Pharmaceutical Abstracts (January 1970-May 2003), and Natural Medicines Comprehensive Database (January 1995-May 2003) using the search terms supplement, herbal, weight loss, obesity, overweight, conjugated linoleic acid, ephedra, ephedrine, chromium, Garcinia cambogia, hydroxycitric acid, chitosan, and pyruvate. STUDY SELECTION: Performed manually by the authors. DATA EXTRACTION: Performed manually by the authors. Only single-agent, randomized, blinded, controlled studies with sufficient scientific rigor in overweight or obese subjects were included. DATA SYNTHESIS: Approximately 50 individual supplemental products and hundreds of combination products are promoted for weight loss. As a result, much confusion exists among health care professionals regarding the efficacy and safety of these products. Results for conjugated linoleic acid were positive in three clinical studies, with few adverse effects. Ephedra has been shown to be effective in promoting weight loss, especially when combined with caffeine, but it has a high adverse effect risk profile. The data regarding ephedra and ephedra combinations are conflicting, and many of the studies were poorly designed. Garcinia and chitosan have not shown much promise for weight loss, but little research has been done. Pyruvate has consistently shown positive weight loss effects. CONCLUSION: Overall, herbal products and dietary supplements promoted for weight loss lack sufficient supporting efficacy and safety data. More research is needed to draw definitive conclusions. Conjugated linoleic acid and pyruvate have the best supporting evidence, but larger and better-controlled trials are needed before pharmacists should recommend these agents to patients seeking to lose weight.